Added new base class TrackedObjectBase, changed class KeyframeBBox to TrackedObjectBBox and changes it's inheritance from KeyframeBase to TrackedObjectBase.
- Added KeyframeBase class
- Adjusted the inheritance of KeyframeBase to KeyframeBBox and Keyframe
- Added feature to attach clip to bounding box
- Added support to select tracked object with a dropdown list and removed keyframebbox downcasting
- Also removed "crop" from Clip class, as it was never implmeneted correctly, and we have a fully functional "crop" effect when needed
- Added caching to Clip class, to optimize previewing of cached frames (much faster than previous)